infix to prefix in c

# include <stdio.h># include <string.h># define MAX 20void infixtoprefix(char infix[20],char prefix[20]);void reverse(char array[30]);char pop();void push(char symbol);int isOperator(char symbol);int prcd(symbol);int top=-1;char stack[MAX];main() {	char infix[20],prefix[20],temp;	printf("Enter infix operation: ");	gets(infix);	infixtoprefix(infix,prefix);	reverse(prefix);	puts((prefix));}//--------------------------------------------------------void infixtoprefix(char infix[20],char prefix[20]) {	int i,j=0;	char symbol;	stack[++top]='#';	reverse(infix);	for (i=0;i<strlen(infix);i++) {		symbol=infix[i];		if (isOperator(symbol)==0) {			prefix[j]=symbol;			j++;		} else {			if (symbol==')') {				push(symbol);			} else if(symbol == '(') {				while (stack[top]!=')') {					prefix[j]=pop();					j++;				}				pop();			} else {				if (prcd(stack[top])<=prcd(symbol)) {					push(symbol);				} else {					while(prcd(stack[top])>=prcd(symbol)) {						prefix[j]=pop();						j++;					}					push(symbol);				}				//end for else			}		}		//end for else	}	//end for for	while (stack[top]!='#') {		prefix[j]=pop();		j++;	}	prefix[j]='\0';}////--------------------------------------------------------void reverse(char array[30]) // for reverse of the given expression {	int i,j;	char temp[100];	for (i=strlen(array)-1,j=0;i+1!=0;--i,++j) {		temp[j]=array[i];	}	temp[j]='\0';	strcpy(array,temp);	return array;}//--------------------------------char pop() {	char a;	a=stack[top];	top--;	return a;}//----------------------------------void push(char symbol) {	top++;	stack[top]=symbol;}//------------------------------------------int prcd(symbol) // returns the value that helps in the precedence {	switch(symbol) {		case '+':		        case '-':		        return 2;		break;		case '*':		        case '/':		        return 4;		break;		case '$':		        case '^':		        return 6;		break;		case '#':		        case '(':		        case ')':		        return 1;		break;	}}//-------------------------------------------------int isOperator(char symbol) {	switch(symbol) {		case '+':		        case '-':		        case '*':		        case '/':		        case '^':		        case '$':		        case '&':		        case '(':		        case ')':		        return 1;		break;		default:		        return 0;		// returns 0 if the symbol is other than given above	}}